A bandgap voltage reference circuit is a circuit generating a reference voltage that is less temperature-dependent on the basis of voltages of semiconductor P-N junctions. The reference voltage is widely used in analog circuits such as A-D converters, D-A converters, DC-DC converters, Low-Dropout (LDO) regulators, and temperature sensors.
The bandgap voltage reference circuit includes P-N junction elements such as bipolar transistors, resistance elements, and a differential amplifier. The bandgap voltage reference circuit combines a P-N junction voltage which has a negative temperature characteristic in which the voltage decreases with increasing temperature and a thermal voltage which has a positive temperature characteristic in which the voltage increases with increasing temperature, thereby canceling out the temperature dependencies of the voltages to generate a reference voltage that is less temperature-dependent.
The bandgap voltage reference circuit typically has two stable operation points: one is a shutdown point at which output voltage is near 0 V (a first stable point) and a second stable point at which a desired voltage is output. Therefore, a startup circuit is provided to prevent the bandgap voltage reference circuit from stopping operation at the first stable point during power-up. The startup circuit forcibly supplies a startup current to the bandgap voltage reference circuit on startup of the bandgap voltage reference circuit to raises the output voltage of the output terminal to a voltage near the second stable point, rather than the first stable point.
A bandgap voltage reference circuit that has such a startup circuit is described in Japanese Laid-Open Patent Publication No. 2006-23920, for example.
Since the startup circuit described above supplies a startup current to the output terminal in order to forcibly raise the output voltage to a desired voltage on startup of the bandgap voltage reference circuit, current consumption is increased. Especially in the case of a circuit that is repeatedly powered on and off, startup current consumed by the startup circuit at each startup is not negligible. Such startup current consumption reduces the battery life of a battery-operated apparatus.